Cooley Spruce Gall Adelgid

If you’ve noticed unusual cone-like growths on your spruce trees, you may be dealing with Cooley spruce gall adelgids—a common pest found throughout Colorado landscapes. These tiny, aphid-like insects rely on both spruce and Douglas-fir trees to complete their lifecycle, often going unnoticed until galls begin to form on branch tips. While the damage is usually more cosmetic than severe, understanding how these pests develop and spread can help you protect the health and appearance of your trees before infestations become more serious.

The Cooley Spruce Gall Adelgid is a type of woolly aphid that targets spruces and Douglas-firs. They need both of these to complete their lifecycles.

Lifecycle of a Cooley Spruce Gall Adelgid

This pest will overwinter in the spruces as immature females. They will remain in the young branches of the trees. Then in the spring, they will mature and lay eggs near the developing buds.

As the eggs hatch, the nymphs will feed on the base of the growing needs, leading to galls developing. The nymphs can then further develop within the galls, before the galls dry out. The bugs will then form wings and fly off to the Douglas-fir trees to continue their development. This happens by the middle of summer.

While on the Douglas-fir trees, they will lay eggs on the needles. Several generations will be produced this time of year, but no galls form on the Douglas-fir.

Some of these newer aphids will develop wings so that they can fly  to the spruce. They then deposit more eggs, which turn into the young females that will overwinter in this form. Others will remain on the Douglas-fir.

The Damage Cooley Spruce Gall Adelgids Cause

For the most part, the pests don’t actually cause a lot of damage. The galls certainly look unsightly and worrisome, but they don’t damage the actual tree.

However, if an infestation becomes heavy, this can create an issue. The tree growth can slow down, and there may be some distortion to the way the needles form.

Controlling the Levels of Cooley Spruce Gall Adelgid

Most people won’t need to do anything to keep the levels of the insect under control. Nature does the job, with a few predators out there eating them. If you want to keep your trees looking pretty or there is a heavy infestation, then you may need to take steps.

The best time to apply treatments is in the fall. The overwintering females will have settled by then, and you can take precautionary steps to make it harder for these females to lay eggs in the spring.

Horticultural oils are used to help with the control, but you’ll need to apply them before the new shoots of needles form on the tree in the spring. You can also use imidacloprid injected into the soil, but this treatment usually does nothing until after galls form.

What is a Cooley spruce gall adelgid?

The Cooley spruce gall adelgid is a small, aphid-like insect that forms cone-shaped galls on spruce trees and also feeds on Douglas-fir trees.

What do spruce galls look like?

Spruce galls look like small pinecones or growths on the tips of branches. They are usually green at first and turn brown as they dry out.

Do Cooley spruce gall adelgids harm trees?

In most cases, they cause minimal damage. However, heavy infestations can slow tree growth and distort needles.

Why do adelgids need two types of trees?

They require both spruce and Douglas-fir trees to complete their lifecycle, moving between them during different stages of development.

When is the best time to treat adelgids?

The best time to treat is in the fall or early spring before new needle growth begins.

How do you control Cooley spruce gall adelgids?

Control methods include:

• Horticultural oils
• Monitoring infestations
• Encouraging natural predators
• Systemic treatments like soil injections (in severe cases)

Should I remove spruce galls?

You can prune out galls for appearance, but it’s not always necessary unless the infestation is severe.

If your spruce or Douglas-fir trees are showing signs of gall formation or pest activity, it may be time to take a closer look. At SprayTech, we specialize in professional tree spraying and pest control solutions designed specifically for Colorado landscapes. Our team can assess your trees and recommend the most effective treatment to keep them healthy and looking their best. Visit treesandweeds.com to request your free estimate and get ahead of potential infestations before they spread.